Generally, in a compaction vehicle are prepared a plurality of kinds of rolls, tires, and the like in accordance with an application and condition of a compaction, and different articles are attached to a front wheel and a rear wheel in some cases; therefore, there exist many variations of vehicle kinds according to a difference of their combination.
FIGS. 7A and 7B are side views showing compaction vehicles often used in a compaction of uneven ground; FIG. 7A shows a vehicle kind where tires are attached as a rear wheel, and a smooth roll is attached as a front wheel; and FIG. 7B shows a vehicle kind where a tamping roll of a large diameter is attached instead of the smooth roll. As a compaction vehicle used in such uneven ground, there is the vehicle where a control apparatus is mounted for determining a slip state from a change of a ratio of respective rotational speeds (rotations per unit time) of front and rear wheels, and for reducing a rotational speed of a slipping wheel, when a front wheel or rear wheel thereof slips in a slush and the like.
According to a conventional control apparatus, a rotational speed ratio is obtained from a ratio of diameters of front and rear wheels, and the ratio is preset as a fixed reference rotational speed ratio. Because each compaction vehicle of FIGS. 7A and 7B has a different rotational speed ratio with each other, the rotational speed ratio of a different value is preset. Then at the same time, a set range determined to be in a non-slip state, that is, an upper limit value and lower limit value of the reference rotational speed ratio are preset as fixed values, respectively. When a rotational speed ratio monitored is out of range of the upper limit value or the lower limit value in a compaction and the like, it is determined that one of the front and rear wheels is slipping. In addition, because the applicants cannot find a proper patent document about a conventional control apparatus applied to a compaction vehicle and monitoring a rotational speed ratio of front and rear wheels, the applicants cite Japanese Patent Laid-Open Publication No. 2001-146928 whose technology eliminates a slip between left and right drive wheels.